"How many Conservative employees have been seconded to the No campaign? Will you declare the full value of their services properly as donations?"

According to the Observer, Mr Huhne called on Baroness Warsi to stop using "secret donations to advance scares and smears".

He added: "Please stop now before you poison our politics".

The two senior government figures started bickering when Baroness Warsi made a speech arguing that AV would help the BNP by giving extremist voters further votes.

That argument prompted an extraordinary backlash, with campaigners pointing out that the BNP were actually opposing AV.

But the most colourful response came from Mr Huhne, who accused Baroness Warsi of acting like "Goebbels".

The two were reported to have continued their row after a Cabinet meeting this week.

But Labour figures, many of whom oppose AV, reacted angrily to Mr Huhne's allusion to Tory support for the 'No to AV' campaign.

"It is utter nonsense. The No-to-AV campaign is supported by a significant majority of Labour members of parliament," Jane Kennedy, former Labour MP for Liverpool Wavertree, said.

Neither the 'yes' or 'no' camps have to reveal their financial supporters until six months after the referendum but the Yes to AV campaign has said 95% of its funds come from the Electoral Reform Society and the Joseph Rowntree Trust.

It has run a long campaign to convince the No to AV campaign to reveal its donors.